The invention relates to a thermally controlled electric switching device, especially a temperature fuse or a temperature limiter, with the additional features of the introductory clause of claim 1.
DE 3735331 C2 discloses a thermally controlled electric switching device in which a switching device comprising a motion contact and fixed contact is arranged on a carrier element. In addition, a meltable element is provided that supports a transmission element before being activated when a trigger temperature is exceeded. When the trigger temperature is exceeded, the material of the meltable element is forced out of its cup-like receptacle at the end of the transmission element.
The solder that escapes during this process can, depending on the installed position of the thermal switching device, affect additional electrical elements of the switching device or other electric components of the device. In particular, the solder beads that form as a result of the escaping solder can impair the thermal switching device and compromise its intended safety function.
To secure the transmission element in its designated position prior to final assembly of the device and to simplify assembly, a ring-shaped collar is provided that enlarges the diameter of the transmission element.
The object of the invention/innovation is to further develop a thermal switching device with the features of the introductory clause of claim 1 in such a way that the risk of electrical interference following activation of the thermal switching device is reduced and, in particular, escaping molten solder is spatially controlled.
This object is solved by the characterizing portion of claim 1. Advantageous enhancements of the invention/innovation result from the subclaims.
It has become evident that, due to the surface tension of the molten solder, an enlargement of the transmission element in the form of a melt material screen advantageously results in the escaping molten solder being uniformly accepted and retained under the screen-like enlargement, as it surrounds the stamp-like end of the transmission element in annular fashion or in the form of individual solder beads, thus remaining beneath the screen provided. Furthermore, because of the melt material screen the prescribed electric air and leakage gap is maintained, even if, as a result of the escaping molten solder, especially the aforementioned molten solder beads, the distance is reduced between electric components, especially between the carrier element for the meltable solder charge, which is filled with material, and the motion contact. This reduction in distance is offset advantageously by the melt material screen.
It is especially advantageous if the melt material screen is arranged on the end of the transmission element facing away from the melt element, so that the transmission element exhibits the overall shape of a mushroom, with a stamp-like segment at its lower end and the screen at its top end.
Advantageously, the diameter of the melt material screen is approximately twice that of the stamp-like segment of the transmission element that dips into the solder. The outer edge of the melt material screen is pulled down in the direction of the molten solder intake, so that a hollow space is formed inside the screen, which can, in an especially advantageous manner, be used to take up molten solder.
In general, the volume of the region beneath the melt material screen and the volume of the expelled molten solder should correspond. The volume beneath the under side of the screen should be greater than the volume of the expelled molten solder, so that the portion of the screen descending onto the molten solder does not press the solder outward in a radial manner, thereby eliminating the beneficial effect of the screen.
The transmission element and the melt material screen, which is advantageously arranged on it in one piece, are both made of an electrically non-conductive material, so as to advantageously lengthen the air gap and guarantee electrical insulation between the motion contact and the molten solder.
A projection supporting the motion contact is arranged on the upper side of the melt material screen; said projection can lock into a recess in the unattached end of the motion contact. Thus, the insertion of the transmission element into the prepared switch can be easily achieved, in that the lower end is inserted into the cup containing the melt solder charge and the motion contact spring element is snapped over the projection. This is a relatively simple assembly procedure, which can also be performed by automated means.
The projection is advantageously cone-shaped. The melt material screen can also be held on the stamp-like segment of the transmission element in a displaceable manner, so that the screen-like transmission element can descend onto the escaping molten solder and encapsulate it. When the transmission element is in its sunken position, the outer edge of the melt material screen should protrude radially above the displaced molten solder material or the molten solder material should be at least partially enclosed beneath the screen-like enlargement.
Advantageously, the undercut beneath the melt material screen is shaped in such a way that fluid molten material running up the stamp-like segment is diverted in its direction of flow after it has entered the undercut. This diversion behavior is particularly important when, in older switching devices, the switch contacts adhere to one another or are slightly soldered together and, when the contacts are separated, the stamp or the transmission element suddenly sinks into the molten material and rapidly forces it upward. The diversion prevents the molten material from spraying outward in radial fashion and adversely affecting electrically sensitive surrounding areas.
Claims 14 and 15 describe the especially advantageous uses of the transmission element of a thermal switching device as an elongation element of electrical air and leakage gaps in the switching device, or as a receptacle and screening element for displaced molten solder.